Filtering unsaturated hydrocarbons using intermetallic nano-clusters

ABSTRACT

A filter such as a cigarette filter having a metal reagent which selectively binds with a gaseous component of a gas stream such as tobacco smoke. The metal reagent comprises nanometer or micrometer size clusters of a transition metal or alloy containing a transition metal. The transition metal can be incorporated in an intermetallic compound such as titanium aluminide or iron aluminide. The metal clusters can be incorporated in or on a support material such as silica gel, porous carbon or a zeolite. The metal reagent can remove the gaseous component by selectively binding to unsaturated hydrocarbons such as 1,3-butadiene. The binding can occur by insertion of a metal atom of the metal reagent into a C—H bond or a C—C bond of the gaseous component.

[0001] The invention relates to filtering of unsaturated hydrocarbonsfrom mainstream cigarette smoke using intermetallic nano-clusters. Thenano-clusters can be incorporated in cigarette filter elements in amanner which selectively removes gaseous components such as1,3-butadiene, isoprene, toluene and the like from mainstream smoke.

[0002] Fresh activated carbon can be used to reduce the level of1,3-butadiene in mainstream cigarette smoke. However, because activatedcarbon is a broad base physical adsorbent of gaseous compounds andremoves a large number of volatile and gas-phase compounds fromcigarette smoke, the result can produce undesired effects on the flavorof the tobacco smoke. Selective filtration, on the other hand, has theadvantage of removing targeted gaseous compounds while minimizing theeffect on flavor of the tobacco smoke.

[0003] According to the invention, small (nanometer or micrometer size)metal or metal alloy clusters can be incorporated in or on a supportmedia (e.g., silica gel, porous carbon, zeolites, etc.) and theresulting filter material can be used to selectively bind to unsaturatedhydrocarbons present in cigarette smoke. In a preferred embodiment,transition metals and metal alloys incorporated into the clusters can beused to remove gaseous components such as 1,3-butadiene from mainstreamcigarette smoke as it passes through a filter containing the supportedreactive metal clusters. The transition metals can include iron andtitanium and alloys containing such elements such as iron alloys,titanium alloys, intermetallic compounds such as iron aluminide ortitanium aluminide or transition metal salts (e.g., Cu, Fe, Zn, Al, Ce,V sulfates and/or phosphates) on high surface area support materials.

[0004] Using state-of-the-art theoretical techniques based on densityfunctional theory and generalized gradient approximation for exchangeand correlation potential, calculations of the binding energies oftrans- and cis-form of butadiene to transition metal atom (Fe) as wellas dimers (Fe₂, FeAl, and Al₂) were carried out. The objective of thestudy was to understand if (1) butadiene binds to these species and, ifso, how the binding varies from one atom to another, (2) if one form ofbutadiene binds more strongly than the other, (3) where do the metalatoms insert and (4) if the structure of butadiene undergoes geometricaltransformation as it binds to metal atoms. The study was carried out tosee if suitable traps can be found for this organic molecule and tosuggest experiments to prove the theoretical predictions.

(1) Geometry of cis- and trans-butadiene as they interact with metalatoms and dimers

[0005] In FIG. 1(a) the trans form of butadiene is given. It is a planarmolecule. An Fe atom inserts into the C—H bond and gains an energy of0.37 eV (see Table 1) over an isolated trans-butadiene and Fe atom.While interacting with the cis-form (FIG. 2), the Fe atom, on the otherhand, attaches to the C—C double bond and the structure becomesthree-dimensional. Energetically, the Fe-butadiene complex in thecis-form is more stable than the trans-form by 0.78 eV. This isparticularly interesting as the trans- and cis-forms of butadiene areenergetically nearly degenerate. Addition of Fe does seem to break thisdegeneracy.

[0006] Fe₂ does not bind to the trans- or cis-form of butadiene (FIG.1(c)) as energetically this is higher than dissociated Fe₂ andbutadiene. FeAl and Al₂ dimers, on the other hand, bind strongly to boththe trans- and cis-forms of butadiene. While the bond between Fe and Alremains intact (see FIGS. 1(d) and 2(c)), that between Al and Al breaks(see FIGS. 1(e) and 2(d)). This is because the Fe—Al bond is strongerthan the Al—Al bond. Nevertheless, a binding energy in excess of 1 eVbetween a metal dimer and butadiene is sufficient. The C—C and C—H bondsin butadiene do not change appreciably as metal atoms are bound to themolecule.

(2) Binding of metal atoms to C₂ and C—H dimers

[0007] From the above discussion it is apparent that a metal atom eitherinserts into the C—H bond or attaches to a C—C bond in butadiene. Ascalculations presented in FIG. 1 and FIG. 2 and Table 1 are very complexand costly, the systematics of transition metal binding to CH and C₂molecules was studied to see which atoms can possibly bond more stronglyto butadiene than Fe. The corresponding energies are given in Table 2.The data indicates that Sc, Ti, V, Co, and Ni are better candidates thanFe whether they prefer to insert into the CH bond or attach to C-C bond.Calculations of Sc, Ti, V, Co, and Ni interacting with the completebutadiene molecule can be carried out to prove this hypothesis.Experimental studies of transition metal atoms and Al reacting withbutadiene in the gas phase can also be carried out. TABLE 1 BindingEnergy (eV) System Trans (FIG. 1) Cis (FIG. 2) C₄H₆ 43.98 43.82 C₄H₆Fe0.37 1.15 C₄H₆Fe₂ — — C₄H₆FeAl 1.35 1.76 C₄H₆Al₂ 2.22 2.03

[0008] TABLE 2 Energetics of M-C₂ and M-CH (M = Sc . . . Ni) in eV ME_(b)(MC₂) E_(b)(MCH) Sc 6.76 9.02 Ti 6.95 6.21 V 7.28 4.95 Cr 4.37 4.08Mn 5.03 3.61 Fe 4.86 4.68 Co 6.16 5.45 Ni 6.74 5.79

[0009] Clusters of nanosize intermetallic powders such as Fe₃Al, FeAl,TiAl, NiAl and Ni₃Al can be obtained by melting and atomizationtechniques. They can be processed by laser evaporation, and or chemicaldecomposition techniques. The powders can be produced in inertatmospheres such as argon or helium, or by bleeding a certain amount ofoxygen, nitrogen, or ammonia to alter the surface property of thepowders. The sizes of the particles may be altered by the residence timeof the laser pulse, cooling time, temperature, etc. For instance, it ispossible to synthesize nanoparticles of controlled size and compositionusing pulsed laser vaporization with controlled condensation (LVCC) in adiffusion cloud chamber under well-defined conditions of temperature andpressure.

[0010] While the invention has been described in detail with referenceto specific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

1. A filter comprising a metal reagent which binds with a gaseouscomponent of a gas stream to remove said gaseous component from said gasstream.
 2. The filter according to claim 1, wherein the filter comprisesa cigarette filter attached to a tobacco rod by tipping paper or themetal reagent is incorporated in one or more cigarette filter partsselected from the group consisting of tipping paper, shaped paperinsert, a plug, a space, or a free-flow sleeve.
 3. The filter accordingto claim 1, wherein the metal reagent selectively binds to unsaturatedhydrocarbons in the gas stream.
 4. The filter according to claim 1,wherein the metal reagent comprises nanometer or micrometer sizeclusters of a transition metal or alloy containing a transition metal ora transitional metal salt.
 5. The filter according to claim 1, whereinthe gaseous component to be removed from said gas stream is1,3-butadiene, isoprene and/or toluene.
 6. The filter according to claim4, wherein said metal reagent is incorporated in cigarette filter paperlocated within a free-flow filter, the filter paper optionally having athree-dimensional shape and/or the filter paper being a liner on theinterior of a hollow tubular element.
 7. The filter according to claim1, wherein said metal reagent is incorporated with cellulose acetatefibers and/or polypropylene fibers forming a plug or a free-flow filterelement.
 8. The filter according to claim 4, wherein said metal reagentis incorporated in or on a support material.
 9. The filter according toclaim 8, wherein said support material comprises silica gel, porouscarbon or a zeolite.
 10. The filter according to claim 4, wherein saidtransition metal includes iron and/or titanium.
 11. The filter accordingto claim 1, wherein said metal reagent comprises nanometer or micrometersize clusters of an iron aluminide or a titanium alumlnide.
 12. Thefilter according to claim 1, wherein a metal atom of the metal reagentbinds to a C—H bond and/or a C—C bond of the gaseous component.
 13. Amethod of manufacturing a filter which is useful for removing a gaseouscomponent of a gas stream, comprising steps of: incorporating a metalreagent in a filter, the metal reagent being effective to bind with agaseous component of a gas stream sufficiently to selectively remove thegaseous component from the gas stream.
 14. The method according to claim13, further comprising attaching the filter to a tobacco rod withtipping paper or the metal reagent is incorporated in one or morecigarette filter parts selected from the group consisting of tippingpaper, shaped paper insert, a plug, a space, or a free-flow sleeve. 15.The method according to claim 14, further comprising a step of attachingthe filter paper within a free-flow filter of a cigarette such as byforming said filter paper into a three-dimensional shape or attachingsaid filter paper as a liner on the interior of a hollow tubular elementor combining said metal reagent with fibers and forming a filter elementfrom said metal reagent and fibers or combining said metal reagent withcellulose and/or polypropylene fibers and forming a plug or free-flowfilter element or incorporating said metal reagent in a cavity of saidfilter.
 16. The method according to claim 13, wherein the metal reagentis effective for removing unsaturated hydrocarbons including1,3-butadiene, isoprene and/or toluene from the gas stream.
 17. Themethod according to claim 13, wherein the metal reagent comprisesnanometer or micrometer size clusters of a transition metal or alloycontaining a transition metal or a transitional metal salt.
 18. Themethod according to claim 17, further comprising a step of loading saidmetal reagent in or on a support material forming a filter element ofthe filter.
 19. The method according to claim 18, wherein the supportmaterial comprises silica gel, porous carbon or a zeolite.
 20. A methodof removing a gaseous component from a gas stream, comprising passingthe gas stream in contact with a filter comprising a metal reagent whichbinds with a gaseous component of the gas stream and removes saidgaseous component from the gas stream.
 21. The method according to claim20, further comprising steps of forming the gas stream by burningtobacco and directing tobacco smoke through the filter such that thecomponent of the gas stream to be removed is brought into contact withthe metal reagent and prevented from reentering the gas stream.
 22. Themethod according to claim 21, wherein the metal reagent is incorporatedin one or more cigarette filter parts selected from the group consistingof filter paper, tipping paper, shaped paper insert, a plug, a space, ora free-flow sleeve, the tobacco smoke being passed through the one ormore filter parts.
 23. The method according to claim 20, wherein themetal reagent is effective to selectively remove unsaturatedhydrocarbons present in the gas stream.
 24. The method according toclaim 20, wherein the metal reagent comprises nanometer or micrometersize clusters of a transition metal or alloy containing a transitionmetal or a transitional metal salt.
 25. The method according to claim20, wherein the filter removes 1,3-butadiene, isoprene and/or toluenefrom the gas stream.
 26. The method according to claim 20, wherein themetal reagent is incorporated in or on a support material selected fromthe group consisting of silica gel, porous carbon or a zeolite.
 27. Themethod according to claim 26, wherein said silica gel has an averageparticle diameter of at least 10 μm or said silica gel is in the form ofparticles having a mesh size of at least 60 and the gas stream is passedthrough a mass of particles of said silica gel.
 28. The method accordingto claim 26, wherein said silica gel is incorporated with celluloseacetate fibers and/or polypropylene fibers and the gas stream is a smokestream from a burning cigarette.
 29. The method according to claim 20,wherein a metal atom of the metal reagent binds to a C—H bond and/or aC—C bond of the gaseous component.
 30. The filter according to claim 1,wherein the metal reagent is a non-oxide metal reagent or a crystallinemetal reagent.
 31. The method according to claim 13, wherein the metalreagent is a non-oxide metal reagent or a crystalline metal reagent.